1. Field of the Invention
The present invention relates to an image forming apparatus and method, a computer program, and a recording medium, and more specifically to, for example, image processing for adjusting the color tone of monochrome images.
2. Description of the Related Art
Recording apparatuses capable of outputting color images include an inkjet recording apparatus having a plurality of color inks. In an apparatus forming an image by subtractive color mixing, such as an inkjet recording apparatus, three colors of cyan (hereinafter referred to as “C”), magenta (hereinafter referred to as “M”), and yellow (hereinafter referred to as “Y”) are generally used as primary colors. Such a color arrangement allows representation of C, M, and Y hues and also representation of, for example, red (hereinafter referred to as “R”) by superposition of M and Y. Further, the ratio of ink colors to be superimposed is adjusted stepwise to express substantially all color spaces. Recently, the inkjet recording technology based on this principle has increasingly been developed, and there is no surprise that the quality of color images comparable to that of silver-halide photographs can be achieved.
In recent inkjet recording apparatuses, as well as an increase in the quality of color images, technical extension to the field of monochrome photography has progressed.
Monochrome photographs are more popular than color photographs particularly for professional or high-end users who pursue artistically high-quality photography. Inkjet printer recording apparatuses capable of providing monochrome images have started to be commercially available.
One of the important characteristics of monochrome photography is the color tone. Monochrome photographs with good color tones are demanded by users, and inventions relating to such monochrome photographs have been proposed (see, for example, Japanese Patent Laid-Open No. 2005-217985). Japanese Patent Laid-Open No. 2005-217985 discloses that a color conversion is performed so that the color of a monochrome image formed on a recording medium can be located, in the a*b* plane of the CIE-L*a*b* space, on one of three sides of or within a triangle defined by three points of (a*, b*)=(0, −3), (a*, b*)=(1, 0), and (a*, b*)=(3, 0). Therefore, high-quality gray-tone representation can be achieved.
Users who pursue artistically high-quality photography not limited to monochrome photography also have a strong desire to output images on various recording media such as glossy paper typically used as photographic output media, paper with low-gloss silky texture, called “semi-gloss” paper, and non-gloss, i.e., matte-finished, paper. Recently, recording media with unique texture particularly suitable for artistic photography and graphic art, called fine-art paper, have become widespread. There are various types of fine-art paper in terms of the surface treatment, e.g., pearl-finishing, the surface pattern, e.g., embossed pattern, the thickness, etc. Users are able to preferentially select a desired glossy surface or texture. The color tone of an unprinted recording medium called “paper white” may also contribute to such variations of gloss or textures.
The adjustment of color tone in an image with respect to recording media having different color tones of paper white has been attempted many times to date, and inventions relating to adjustment techniques have been proposed (see, for example, Japanese Patent Laid-Open Nos. 2000-13620 and 2005-64841). Japanese Patent Laid-Open No. 2000-13620 discloses that in color matching of recording media having different color tones of paper white, the amount of displacement of a color near paper white is reduced according to the deviation from paper white. Japanese Patent Laid-Open No. 2005-64841 discloses that when paper white is different from reference white, an adjustment coefficient obtained by dividing the XYZ values of reference white by the XYZ values of paper white is used to create a color profile.
If both desires for outputting a recorded monochrome photograph with good color tones and for outputting a monochrome photograph on various recording media having different color tones of paper white are satisfied, the following problem arises.
That is, when a monochrome photograph is output on different recording media, even if the color tone of intermediate levels is matched using a calorimeter, due to the influence of the color tones of paper white of the individual recording media, a color may be viewed differently, thus giving a visually unnatural impression. If a color tone is changed in accordance with paper white, on the other hand, the color tone may not be viewed identically on recording media having different color tones of paper white.
Japanese Patent Laid-Open No. 2005-217985 discloses a system relating to the adjustment of color tone so that a monochrome image with good color tones can be produced on a specific recording medium, but not relating to the adjustment of color tone of a monochrome image between a plurality of recording media having different color tones of paper white. Japanese Patent Laid-Open Nos. 2000-13620 and 2005-64841 do not mention a monochrome mode, and do not disclose the adjustment of color tone in a monochrome image. Japanese Patent Laid-Open Nos. 2000-13620 and 2005-64841 do not mention the adjustment of monochrome color tone between recording media having different color tones of paper white.